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Investment gains (losses) - Narrative (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Gain (Loss) on Securities [Line Items] |  |  |  |
Sales of equity securities |  |  | $ 24,046 | $ 133,218
Taxable gains (losses) on sales of equity securities | $ 10,400 | $ 23,400 | $ 18,700 | $ 97,100

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- Definition Amount of cash inflow from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as investing activity. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 19 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-19 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 45 -Paragraph 1 -SubTopic 10 -Topic 321 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479567/321-10-45-1 + Details
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